Various types of microphones are known that acquire and output sound. One of the types is called a handset microphone, which can transmit speech when a transmission switch is turned on and cannot transmit speech when the transmission switch is turned off (see Japanese Patent No. 3857591). The transmission switch of a handset microphone is generally implemented by, for example, a push switch. The push switch of the handset microphone is continued to be pressed during speech transmission. The push switch is returned to the original state (i.e., not pressed) to stop speech transmission. The contact of the push switch is mechanically opened or closed.
Mechanical turning on/off operation of the contact of the switch readily generates noise. In order to prevent such noise contamination, mechanical contact may be replaced with a reed switch openable or closable by the movement of a magnet attached to a switch knob.
Use of a reed switch as an operation switch of a handset microphone can prevent noise caused at a start or stop operation of speech transmission. A reed switch having contact operated by a magnetic field may however malfunction in an unintentional magnetic field from the exterior.
Handset microphones are often used for radio communication machines and usually transmit radio waves in cooperation with switch operations. In such a radio communication machine, a malfunction of the switch in the handset microphone is caused by an external magnetic field and then leads to undesirable transmission of radio waves.